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SubjectRe: [PATCH v4 10/10] x86-64: Add CONFIG_UNSAFE_VSYSCALLS to feature-removal-schedule
On Tue, May 31, 2011 at 2:34 PM, Andi Kleen <> wrote:
>> +What:        CONFIG_UNSAFE_VSYSCALLS (x86_64)
>> +When:        When glibc 2.14 or newer is ubitquitous.  Perhaps mid-2012.
>> +Why: Having user-executable code at a fixed address is a security problem.
>> +     Turning off CONFIG_UNSAFE_VSYSCALLS mostly removes the risk but will
>> +     make the time() function slower on glibc versions 2.13 and below.
> I disagree with this description (and the whole idea really)
> First it's time+gettimeofday+vgetcu, not just time.
> A more accurate description is
> "will make all x86-64 Linux programs written to the original pre
> vDSO syscall ABI significantly slower"

Well, if this series goes in, then gettimeofday and getcpu are already
slower. It's just time that would get even slower later on.

> And the assumption that all world is using glibc is still as bad
> as it was on the first

As opposed to?

uclibc and klibc don't appear to use vsyscalls or the vdso.

dietlibc is hardcoded to use the vsyscall. Are there any
performance-critical programs using dietlibc?

I don't think that Bionic runs on any released x86-64 systems.

> And it's still a bad idea. Especially since there's a much better
> alternative anyways for the "security problem" which has none of
> these drawbacks.

What's the alternative?

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